This research project will continue the elucidation of the molecular pathogenesis of AIDS-associated non- Hodgkin lymphoma (AIDS-NHL). We will also construct mouse models of AIDS-NHL to validate the >athogenetic role of the identified genetic lesions in vivo, and to serve as preclinical modelsfor testing novel herapeutic strategies. Based on the recent identification of novel abnormalities (ASHM, BLIMP1 inactivation, and BCL6/cMYCinteraction) with clear pathogenetic significance, and on an available panel of tumor biopsies (-50) representative of the major AIDS-NHL subtypes, we plan the following Specific Aims for the next 5 years: 1) Identification of additional genes targeted by ASHM in AIDS-DLBCLand AIDS-BL by high-throughput sequencing of the 5' region of expressed genes (~ 500; data available from Klein et al. 2003). This study will also allowthe identification of: a) recurrent mutations of potential functional significance; b) combinatorial jattems of genetic alterations, leading to the identification of altered pathways. 2) Analysisof BLIMP1 inactivation in AIDS-NHL. Analogous to DLBCL of the immunocompetent host, AIDS- DLBCL (4/20) werefound to display biallelic BLIMP1 inactivation. This study will be extended to the full AIDS-NHL panel to include analysis of chromosomal deletions (by FISH), intragenic deletions and frameshift mutations (by DMAsequencing), and epigenetic inactivation (by promoter methylation analysis). 3) Distribution and pathogenetic role of the abnormal BCL6/cMYC complex in AIDS-NHL. We will analyze the co-expression(by two-color immunohistochemistry) and physical interaction (by co-immunoprecipitation assays) of BCL6 and cMYC in AIDS-NHL. To explore the function of the abnormal BCL6/cMYC complex, we will integrategene expression profile analysis, "ChlP-on-Chip" analysis (to determine promoter binding), and reverse engineering tools (to determine functional relationship) to identify gene expression patterns specifically associated with this complex in AIDS-NHL. These studies will be complemented by additional ones (separateproject) aimed at designing small molecules interfering with the BCLG-cMYC binding, atumor specific target necessary for tumor survival. 4) Construction of mouse models of AIDS-DLBCL and AIDS-BL. Based on the gene alterations identified in Aims 1-3, wewill construct mouse models recapitulating the lesions found in human AIDS-NHL by crossing mouse strains carrying individual gene alterations (cMYC, PIM1, BLIMP1, BCL6). These models will be used for a) testing the effect of chronic antigenic stimulation (by repeated immunization with pleiotropic antigens such as sheep red blood cells) and immunodeficiency (by crossing with CD4-/- mice); b) pre-clinical testing of small molecules generated against the BCL6/cMYC interface (see 3).